Stripe rust of wheat is typically uncommon in Illinois. This year, the cool and moist weather has been favorable for the development of stripe rust, and this disease has been reported at various locations in the southern half of Illinois over the past 2 weeks. Pro-gress of stripe rust should stop if the weather becomes hot and dry, but severity and incidence of this disease may increase if the weather stays cool and moist.
Stripe rust (also called yellow rust) was reported in early to mid-May 2 to 3 weeks ago in Arkansas, Oklahoma, western Tennessee, and southwestern Missouri (http://www.cdl.umn.edu/crb/2003crb/03crb5.html). The spores of the stripe rust fungus have likely been blown up from these southern states to Illinois, where the environmental conditions have favored its infection and spread. Minor levels of this disease were reported in central Illinois in 2000 and 2001, and in southern Wisconsin in 2001. This year, reports suggest stripe rust is common in many areas and may be severe enough in some fields (such as western Macoupin County) to potentially cause yield loss.
Stripe rust often appears earlier in the season than leaf and stem rust of wheat. These different types of rust on wheat are distinguished by the color and pattern of the infected areas. The stripe rust pustules are more yellow than rusty brown and usually appear closely arranged in yellow stripes parallel to veins on leaves. Heads may also be infected with the yellow pustules. The pustules of leaf and stem rust are dark to light red-brown in color and are scattered in an arbitrary pattern over the leaves or stems.
Stripe rust of wheat. (Photo courtesy of Bob Bowden, Kansas State University.)
Leaf rust of wheat. (Photo courtesy of Bob Bowden, Kansas State University.)
Development and spread of stripe rust is strongly influenced by climate, and weather conditions are typically too warm and/or dry in most of Illinois after mid-May to favor this disease. Stripe rust develops most rapidly when temperatures are between 50° and 60°F, and stops when temperatures exceed 70°F. Stripe rust can develop and spread quickly when weather is cool with frequent dew or rainfall.
Another factor that has contributed to increased incidence of stripe rust in parts of the United States is new races of the stripe rust fungus (Puccinia striiformis). At this point, we don't know which races may be most common in Illinois although it is reasonable to consider that the common race(s) in states south and west of Illinois may also become common in Illinois.
Stripe rust can be managed with fungicides and to some degree with wheat varieties that differ in susceptibility. Fungicides labeled for control of stripe rust include Tilt, PropiMax, Quadris, Headline, and Stratego. None of these compounds can be applied after flowering (Feekes growth stage 10.5), and some cannot be applied after the ligule of the flag leaf emerges (Feekes growth stage 8). Product labels should be consulted for proper application of fungicides. It is too late to apply fungicides in many Illinois wheat fields. All of these compounds are systemic. If stripe rust is observed in fields with high yield potential prior to the end of the application period allowed on the label, the decision of whether or not to apply a fungicide should be made quickly because the disease has the potential to develop rapidly if weather conditions are favorable.--Dean Malvick